The present invention relates to a lifting assembly for a lift truck with a lifting mast having at least one mast frame and a load part, as well as a lift drive having at least one lifting chain that lifts the mast frame. The lifting chain is attached to the mast frame at a connecting point and is guided across a deflection point. Such lifting assemblies are used for lift trucks, in particular fork lifts.
Lift trucks, or respectively forklifts, with a lifting assembly have lifting masts which make it possible to lift and lower payloads. The lifting masts possess a plurality of mast frames which are mounted and guided within each other, as well as a load part which is usually provided with fork arms. By using a plurality of mast frames, a particularly favorable ratio is achieved of construction height to lift height. Typically, the lifting masts possess two or more mast frames, wherein a common lifting mast consists of three mass frames, i.e., an inner mast frame, a middle mast frame, and an outer mast or column. Such a lifting mast is termed a triple mast. The functioning of such a lifting assembly will be explained with reference to such a triple mast.
The mast frames are driven by means of lift cylinders and lifting chains which initiate to the lifting process. It was revealed that such a combination of lift cylinders and lifting chains yields the greatest advantages. Practically speaking, a lifting chain is a cable because it is able to transmit exclusively tractive forces. The lifting chain is fastened at both ends to connecting elements on the corresponding components, wherein one component is the associated mast frame. Between the connecting points, the lifting chains are deflected at a deflection point with the assistance of one or more chain rollers. The deflection points are chosen to satisfy the lifting function. Normally, such lifting chains consist of metal materials.
With the triple mast, the middle mast frame is, e.g., lifted with two mast lifting cylinders, whereas the inner mast frame is lifted with two mast lifting chains. The load part is lifted with assistance of a free lift cylinder and a free lift chain. The mast lifting chains are fastened at the bottom end of the inner mast frame to connecting points. They are deflected at the top end of the middle mast frame at deflection points by means of chain rollers. The other ends of the lifting chains are fastened in the outer column to connecting points.
During the operation of such lift trucks, or respectively forklifts, the lifting chains oscillate while driving due to unevenness in the roadway. Such oscillation can cause the lifting chains to strike the adjacent components, in particular the associated mast frame. This produces undesirable noise and damage to the mast frame. The noise generated by the chains is produced as individual, sometimes rapid, sequential loud blows.
A mast assembly for a lift truck is known from DE 198 55 202 B4, which has a support for holding a load lifting device, a lift drive for lifting the support with a lifting chain connected to the support, a guide mast on which the support is guided, and a oscillation limiter arranged on the guide mast to limit the oscillating movement of the lifting chain. The oscillation limiter is a type of guide for the lifting chain, i.e., a relative movement occurs between the oscillation limiter and lifting chain. To allow the chain to move past the oscillation limiter, a distance between the components is required, whereby the chain can also still swing within the overlapping area with the oscillation limiter. In this context, the oscillation limiter is attached to the outer mast (column). As mentioned above, the lifting chain and oscillation limiter execute a relative movement in relation to each other.